1. Field of the Invention:
This invention relates to a pipe joint, and is more particularly concerned with a relaying pipe joint employed during the connecting of synthetic resinous products, such as synthetic resinous pipe, with metallic wares, such as metal pipe and other universal metallic parts. This invention is to be preferably applied to city water supply, agricultural irrigation piping, general interior pipe laying, indoor hot water plumbing and the like.
2. Description of the Prior Art:
Normally, the use of metallic pipe joint for connecting metallic pipes with each other and, likewise, the employment of synthetic resinous pipe joint or metallic pipe joint for fastening synthetic resinous pipes, respectively have been passed for a matter of common knowledge in the field of piping technique. The reason for this was that the pipe connecting portion is the one which is most susceptible to influences resulting from thrust due to tension and compression which are pipe-axially working, earthen pressure that is acting in the intersecting direction with the pipe axis at the time of pipe laying underground, and fluid pressure that is caused by liquid flowing through the pipe, from whence the thought that it is regarded as appropriate for a pipe-connecting part to use pipe joint which is much more strong than, or at least as strong as, the main pipe, has been prevalent heretofore. Consequently, it was an usual manner to use a metallic pipe joint, in the case where confronted with necessity, to connect a metallic pipe with a synthetic resinous one.
There was, however, a weak point in this method by which synthetic resinous pipe was to be connected with metallic pipe joint, that because of susceptibility to influences of adhesives or of the difference in the rate of thermal expansion which were produced by contact of heterogeneous materials, the reliability on water-tightness was not too high; after all, sufficient water-tightness would not be obtained, excepting some kind of mechanical joint which is liable to count on mechanical tightening force; and yet, too much intensification of this mechanical tightening force brought about a risk of breakage of synthetic resinous pipe by the tightening pressure itself.
To ward off this disadvantage, it was common to practice with relatively weak tightening, nevertheless, there happened sometimes separation accident or leakage trouble in the pipe connecting part.
A mechanical joint is composed not of an integral piece, but of various parts, such as seal packing, snap, bolt, nut and so on, with the result that annoying parts control and troublesome connecting operation are unpopular among piping workers. In spite of diverse ideas proposed, a completely satisfactory improvement has not been found yet.
On the other hand, as the field of application of synthetic resinous pipe has now been much enlarged, a variety of studies on synthetic resinous pipe joint has been greatly promoted, thus entailing a substantial amelioration of its impact strength, tensile strength, resistance to wear, etc., as the result of accumulation of designs and contrivances of its form, of wall thickness, and of condition of injection-molding. It has thus become general knowledge to use synthetic resinous pipe joint for connecting synthetic resinous pipe each between the other. Thus, it can be said that a great prospect is open to synthetic resinous pipe joint which is superior to others in economical efficiency, lightness of weight, workability and so forth. In this way, expectation for synthetic resinous pipe joint grows greater and a strong tendency to try to use it appears in part, while the following problems remain unsolved as to existing synthetic resinous pipe joint.
FIG. 1 shows a perspective view of a conventional synthetic resinous pipe joint now generally in use. From left to right, there are seen a male screw, or externally threaded portion, 1, a nut-shaped tightener 2 and a faucet 3. FIG. 2 shows a partly cutaway side view, illustrating a state of connection of a metallic pipe A with a synthetic resinous pipe C by the use of the abovedepicted pipe joint B, wherein the metallic pipe A and the pipe joint B are threadably connected, and the synthetic resinous pipe C and the pipe joint B are connected by means of adhesive. Their screw-connecting is performed by rotating, while holding the metallic pipe A stationary, the nut-shaped tightener 2 with a monkey spanner, single head, or adjustable wrench. On this occasion, the female screw or internally threaded end portion of the metallic pipe A and the male screw or externally threaded portion of the synthetic resinous pipe joint B rub heavily against each other over their corresponding thread faces because of a tapering, or narrowing toward the end, shape of the male screw of the synthetic resinous pipe joint B, thereby causing created stress to concentrate on the synthetic resinous male screw which is inferior in strength, even in the presence of a slight dimensional error. As a result, cracks occur, as does twist-off, friction loss, and so on, while on the surface 2a of the nut-shaped tightener 2, clasped by the monkey spanner or the like, abrasion or breakage occurs. Even if there are no dimensional errors, as previously mentioned, operation would be very unreliable in regard to safety, because when piping for a hot water supply or in the hottest and coldest territories, dimensional disaccordance occurs now and then, resulting from the differences between rates of thermal expansion of both materials. Even in the case that their dimensions happen to be in accord with each other, so they could be connected without excessive load, differential gaps will be induced to their thread faces from time to time owing to thermal changes after the conclusion of connection, and consequently, reliability in their water-tightness cannot help becoming remarkably low. Also, vibration and the like of pipe body, produced by pipe axial tension and compression, or bending load due to earthen pressure, and more pulsation pressure of flowing water are not negligible effects during long-term use. By dint of these effects, there occurs even a possibility to lead to the very failure of the pipe joint due to cracks created in the root of the thread.